Milling cutters for machining structural components are well known in the prior art. However, such structural components as those used, for example, in aircraft are usually thin in cross-section and have deep pockets. Such parts are generally machined from a large, solid block of a strong, lightweight metal such as titanium. Often, more material is removed from the block of metal than remains in the finished workpiece. The most common method for machining such structural components is to use a drill in combination with a milling cutter. The drill is used to form access holes of a predetermined depth equal to the depth of the pocket to be formed. The milling cutter is then lowered into the access hole and moved back and forth over the workpiece in the same plane until the entire cross-sectional area of the pocket being formed has been traversed. The cutter is then lowered further into the access hole and the process is repeated as many times as necessary to form a pocket of the desired depth. Such a prior art technique is, of course, very time consuming. Two separate machining operations are required for every pocket (i.e., drilling and milling). Since the depth of cut which conventional milling cutters are capable of making is usually small in relation to the depth of the pocket being formed, many passes over the workpiece are required to achieve the desired pocket depth.
While there are milling cutters capable of performing both plunge and face milling operations, such cutters are not without their limitations. For example, when the same milling cutter is used to perform both plunge and face milling operations, the cutting inserts mounted in the cutter head are simultaneously subjected to large axial, radial and tangential forces. In order to prevent the inserts in the cutter head from axial, radial, or tangential movement during the cutting operation, the seats in such prior art cutters are complementary in shape to the inserts that they receive so that their upper and side edges securely engage and mate with the transverse edge and side edge of the inserts, respectively. Such an arrangement, however, allows the milling head to accommodate only one particular shape of cutting inserts. Hence, a different milling cutter must be used whenever a differently shaped cut is desired, such as when corners of a smaller or larger radius between the sidewalls and floor of the cut are required.
Clearly, what is needed is a milling cutter capable of effectively cutting deep pockets in a workpiece in both the vertical and transverse direction in order to obviate the need for separate drilling and milling operations in the workpiece. Ideally, the same cutter head would be able to accommodate inserts having different shapes so that the same milling cutter could be used to make differently shaped cuts in the workpiece, such as differently-radiused corners between the sidewalls and the floor of the cut. The insert seats should be designed for positively securing the inserts against axial, radial, or tangential movement during the cutting operation, which could create an unsatisfactorily rough cut and cause undue wear on the cutting edges of the inserts. The milling cutter and inserts should be designed so that the cutter is capable of making a deep vertical cut in relation to its size. Additionally, a positive rake angle should be maintained on the cutting edges for both vertical and lateral cutting of the workpiece both to reduce the power necessary to machine the workpiece, and to maximize the life of the cutting edges of the inserts.